Method and apparatus for network-controlled proximity device to device discovery and communication

ABSTRACT

A method, apparatus and computer program in which an apparatus exchanges wirelessly information with a public land mobile network. The apparatus detects a wireless device to device discovery initiation instruction from the public land mobile network and responsively: sends one or more wireless discovery signal transmissions for a peer device or to monitor wireless discovery signal transmissions sent by a peer device; and directly communicates wirelessly with a peer device that indicates having received the wireless discovery signal transmission or from which the apparatus has detected a wireless discovery signal transmission in result of the monitoring of wireless discovery signal transmissions.

TECHNICAL FIELD

The present application generally relates to network-controlledproximity device to device discovery and communication.

BACKGROUND

Cellular networks operate within their coverage area so that radiosignals are sent solely between each mobile telephone and one or morebase stations. However, there are occasions in which one mobiletelephone is out of coverage of the base stations. Emergency calls canyet be made through any operator so that network coverage can be foundthrough another operator on calling to an emergency phone number.

SUMMARY

Various aspects of examples of the invention are set out in the claims.

According to a first example aspect of the present invention there isprovided an apparatus comprising:

-   -   a wireless communication interface configured to exchange        information with a public land mobile network; and    -   at least one processor configured to control operation of the        apparatus;    -   wherein the at least one processor is configured to detect a        device to device discovery initiation instruction from the        public land mobile network and to responsively:        -   cause the wireless communication interface to send one or            more discovery signal transmissions for a peer device or to            monitor discovery signal transmissions sent by a peer            device; and        -   to cause communicating directly, using the wireless            communication interface, with a peer device that indicates            having received the discovery signal transmission or from            which the apparatus has detected a discovery signal            transmission in result of the monitoring of discovery signal            transmissions.

According to a second example aspect of the present invention there isprovided a method comprising:

-   -   exchanging wirelessly by an apparatus information with a public        land mobile network;    -   detecting by the apparatus a wireless device to device discovery        initiation instruction from the public land mobile network and        responsively:        -   send by the apparatus one or more wireless discovery signal            transmissions for a peer device or to monitor wireless            discovery signal transmissions sent by a peer device; and        -   to directly communicate wirelessly with a peer device that            indicates having received the wireless discovery signal            transmission or from which the apparatus has detected a            wireless discovery signal transmission in result of the            monitoring of wireless discovery signal transmissions.

According to a third example aspect of the present invention there isprovided an apparatus comprising

-   -   a processor configured to cause the apparatus to:        -   exchange wirelessly information with a public land mobile            network;        -   detect a wireless device to device discovery initiation            instruction from the public land mobile network and            responsively:            -   send one or more wireless discovery signal transmissions                for a peer device or to monitor wireless discovery                signal transmissions sent by a peer device; and            -   to directly communicate wirelessly with a peer device                that indicates having received the wireless discovery                signal transmission or from which the apparatus has                detected a wireless discovery signal transmission in                result of the monitoring of wireless discovery signal                transmissions.

According to a fourth example aspect of the present invention there isprovided an apparatus comprising:

-   -   at least one processor; and    -   at least one memory including computer program code;    -   the at least one memory and the computer program code configured        to, with the at least one processor, cause the apparatus to        perform at least the following:        -   exchange wirelessly information with a public land mobile            network;        -   detect a wireless device to device discovery initiation            instruction from the public land mobile network and            responsively:            -   send one or more wireless discovery signal transmissions                for a peer device or to monitor wireless discovery                signal transmissions sent by a peer device; and            -   to directly communicate wirelessly with a peer device                that indicates having received the wireless discovery                signal transmission or from which the apparatus has                detected a wireless discovery signal transmission in                result of the monitoring of wireless discovery signal                transmissions.

According to a fifth example aspect of the present invention there isprovided a computer program comprising:

-   -   code for exchanging wirelessly information with a public land        mobile network;    -   code for detecting a wireless device to device discovery        initiation instruction from the public land mobile network and        responsively:        -   sending one or more wireless discovery signal transmissions            for a peer device or to monitor wireless discovery signal            transmissions sent by a peer device; and        -   directly communicating wirelessly with a peer device that            indicates having received the wireless discovery signal            transmission or from which the apparatus has detected a            wireless discovery signal transmission in result of the            monitoring of wireless discovery signal transmissions.    -   when the computer program is run on a processor.

According to a sixth example aspect there is provided a computerreadable memory medium comprising the computer program of the fifthexample aspect.

The computer readable memory medium of the sixth example aspect, whereinthe memory medium is a non-transitory memory medium.

Any foregoing memory medium may comprise a digital data storage such asa data disc or diskette, optical storage, magnetic storage, holographicstorage, opto-magnetic storage, phase-change memory, resistive randomaccess memory, magnetic random access memory, solid-electrolyte memory,ferroelectric random access memory, organic memory or polymer memory.The memory medium may be formed into a device without other substantialfunctions than storing memory or it may be formed as part of a devicewith other functions, including but not limited to a memory of acomputer, a chip set, and a sub assembly of an electronic device.

According to a seventh example aspect of the present invention there isprovided a method comprising:

-   -   exchanging by an apparatus information with a public land mobile        network using a first radio transceiver;    -   discovering a proximate peer device by the apparatus using a        second radio transceiver operating with a radio system other        than the public land mobile network and responsively requesting        with the first radio transceiver from the public land mobile        network for permission to provide the discovered peer device        with an access to a cellular service through the apparatus;    -   detecting by the apparatus a wireless device to device        communication permission from the public land mobile network and        responsively:        -   starting to relay information between the public land mobile            network and the peer device using the first and second radio            transceivers, respectively.

According to an eighth example aspect of the present invention there isprovided an apparatus comprising:

-   -   a memory comprising computer program code; and    -   at least one processor configured to cause the apparatus to        perform according to the program code the method of the seventh        example aspect.

Different non-binding example aspects and embodiments of the presentinvention have been illustrated in the foregoing. The embodiments in theforegoing are used merely to explain selected aspects or steps that maybe utilized in implementations of the present invention. Someembodiments may be presented only with reference to certain exampleaspects of the invention. It should be appreciated that correspondingembodiments may apply to other example aspects as well.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of example embodiments of the presentinvention, reference is now made to the following descriptions taken inconnection with the accompanying drawings in which:

FIG. 1 shows an architectural overview of a system of an exampleembodiment of the invention;

FIG. 2 shows a flow chart illustrating an example embodiment of theinvention, using long term evolution as an example system;

FIG. 3 shows a negotiation process according to one example embodiment;

FIG. 4 shows a flow chart illustrating an example embodiment of theinvention;

FIG. 5 shows a block diagram of an apparatus suited for operating as theuser equipment in FIG. 1; and

FIG. 6 shows a block diagram of an apparatus suited for operating as anetwork element such as base station or base station controller.

DETAILED DESCRIPTION OF THE DRAWINGS

An example embodiment of the present invention and its potentialadvantages are understood by referring to FIGS. 1 through 6 of thedrawings.

FIG. 1 shows an architectural overview of a system 100 of an exampleembodiment of the invention. The system 100 comprises a first publicland mobile network (PLMN) 110 that has a plurality of base stations 120and wireless mobile communication devices or user equipment (UE) 130,two of which are labeled as a first user equipment or UE1 and as asecond user equipment or UE2 in sake of simpler discussion of somefunctions. The system 100 also comprises a second PLMN 140 withrespective base stations 150 and user equipment 160. The second PLMN 140and associated other elements are drawn with dashed lines so that theelements that operate in or with the first PLMN 110 are easier toidentify.

In an example embodiment, the PLMNs are any of Global System for Mobilecommunications; wideband code division multiple access (W-CDMA); LongTerm Evolution (LTE) or 4G; Interim Standard 95; CDMA2000; PersonalDigital Cellular, for example. The PLMN may support circuit switchedconnections, packet switched connections or both alternatingly and/orsimultaneously. The first and second PLMNs 110, 140 need not be of sametype. It is also understood that some or all of the user equipment 130can be multi-mode devices capable to operate with many different typesof PLMNs including those used by the first and second PLMN 110, 140. Thenetwork with which each user equipment works can be determined by asubscription e.g. as defined by a subscriber identity module of anyknown type.

FIG. 1 also shows an illustrative first coverage 170 for the first PLMN110 and a second coverage 180 for the second PLMN 140. The firstcoverage 170 contains a first user equipment UE1 but not a second userequipment UE2 that is relatively near the first user equipment UE2. Thecoverage of each PLMN can be determined by the operators of respectivePLMN e.g. using measurement data received from moving user equipment andlocation of the user equipment either as determined by the userequipment themselves or by the PLMN.

In FIG. 1, the first user equipment UE1 and the second user equipmentUE2 are that near that a device to device (D2D) link could be formedbetween them, as will be described in the following. The devicescommunicating directly with one another or attempting to communicatedirectly with one another, i.e. without the communications travellingthrough a base station of the PLMN, can be referred to as peer devicesor peer apparatuses.

FIG. 1 also shows a server 190 communicatively connected with the firstPLMN 110 that is used in the following to describe some exampleembodiments.

FIG. 2 shows a flow chart illustrating an example embodiment of theinvention, using LTE as an example system.

In beginning, the first user equipment UE1 is connected to the network,210. It is then identified 220 whether the first user equipment UE1 isnear an edge of the coverage edge (i.e. near first coverage 170 edge inFIG. 1). This step can be performed, depending on embodiment, by eitheror both of the first user equipment 130 and the network. Notice thatwhile the signaling is drawn to end at the base station or eNB interminology used in LTE, the related operations can be performed fartherin the LTE network if not at the eNB itself. In sake of simplicity, thefollowing description is made so that communications with the basestation or eNB are equaled to communications with the network.

User equipment based identification of proximity to a coverage edge canbe detected, for instance, by deducing from signal strengths of receivedpilot signals sent by base stations of the network, by comparing thelocation of the user equipment to known coverage area of the network,and/or by comparing current active set of base stations to a predefinedset. The user equipment may comprise a positioning circuitry and/orreceive position information from auxiliary devices and/or from thenetwork.

Network based identification of proximity to a coverage edge can bedetected, for instance, from the signal strength of uplinkcommunications sent by the user equipment to the serving base station,possibly in combination with received signal strengths detected by otherbase stations in the network for signals originating from the userequipment. Instead of measuring signal strength, the commanded powerlevel in itself can be used as a measure of signal attenuation and thusof distance. The network can also or alternatively be configured toperform network based positioning and to compare the location of theuser equipment to known coverage area of the network.

The network 120 then requests the user equipment to start operating in adiscovery mode. In FIG. 2, this discovery mode is such that the firstuser equipment UE1 sends one or more discovery advertisement or beaconsignals indicating its presence for other user equipment such as thesecond user equipment UE2. Hence, the network 120 requests 230 the firstuser equipment UE1 to start transmitting the discovery signal(s) andresponsively the first user equipment UE1 sends one or more discoverytransmission signals.

The identification of user equipment close to coverage edge andrequesting of user equipment to start operating in the discovery modecan be performed with signals specifically concerning given userequipment, i.e. one or more devices. In an alternative exampleembodiment, the network broadcasts or otherwise provides the userequipment with criteria that the user equipment then monitor(s) whenoperating. Once the criteria are met in given user equipment such as thefirst user equipment UE1, the user equipment in question startsoperating in the discovery mode. In an example embodiment, this startingis also signaled to the network 120. Armed with this knowledge, thenetwork 120 can change its operation so that no further user equipmentare requested either directly or via defined criteria to start operatingin the discovery mode in the proximity of the user equipment that is orare already so operating. In an example embodiment, the networkselectively chooses which UEs are going to transmit beacon signals incertain area.

The second user equipment UE2 that is outside the coverage of thenetwork 120 then detects 250 the discovery signal transmission from thefirst user equipment UE1. In response, the second user equipment UE2sends a discovery signal detection message to the first user equipmentUE1. The sending of this discovery signal detection message can indicatethat the second user equipment UE2 desires to start a device to devicelink.

Cellular access via device to device link is next negotiated 270 (seeFIG. 3), if the second user equipment UE2 has indicated a desire to doso by the discovery signal detected message. In an example embodiment,this discovery signal detected message contains a flag that enables thesecond user equipment UE2 to indicate if it desires to start thenegotiation, if it does not desire to start the negotiation, or whetherit desires or not to start the negotiation.

The discovery signal detected message can also be formed to contain anidentifier of the second user equipment UE2. In an example embodiment,the first user equipment UE1 forwards that identifier to the networkeven if the second user equipment would not have indicated desire forstarting the negotiation for cellular access via device to devicecommunication. The network 120, being aware of an out-of-coverage deviceor the second user equipment UE2, can then instruct more frequentdiscovery processing using one or more user equipment (such as the firstuser equipment UE1) than if the network is not aware of any device beingoutside its coverage area. The network can also be configured, as in oneexample embodiment, to monitor deteriorating signals of user equipmentand so determine if given user equipment leaves the network coverage.This information can likewise be used by the network to increase thefrequency of device discovery processes by proximate other userequipment that remain within the network coverage.

After cellular access via device to device link has been negotiated 270,the second user equipment UE2 accesses 280 one or more cellular servicesvia the first user equipment UE1.

Before turning to the negotiation 270 of the device to device link withreference to FIG. 3, some considerations are next discussed relating tothe cellular access via device to device link of different userequipment (UE1, UE2).

Depending on the PLMN techniques in question, the user equipment is/areconfigured in any of different ways so that two different user equipmentcan communicate directly with one another. In time division duplexsystems, this can be simply performed so that one user equipmenttransmits during a period that is normally reserved for downlinkcommunications. In frequency division duplex systems, the transmittercan be configured to operate in the normal downlink frequency band orthe receiver can be configured to operate in the normal uplink frequencyband. Further still, the user equipment can be configured to operate inan auxiliary radio band not normally used for either of the uplink ordownlink (e.g. using Private Mobile Radio (PMR) frequencies).

In the embodiments in which cellular communication channels are beingused for device to device communications, the network can be configuredto define parameters that the user equipment must use e.g. for avoidingof interference for the network and/or for other networks. Theparameters contain in one example embodiment any one or more of: thefrequency or frequencies to be used; a frequency hopping scheme;spreading code; scrambling code; time slot or time slots; allocationtime; allocation period; link parameters such as modulation/codingscheme and data rate.

FIG. 3 shows the negotiation process 270 according to one exampleembodiment.

An association request is sent from the first user equipment UE1 to thesecond user equipment UE2, 310. The association request containsencryption information. In an example embodiment, where the second userequipment UE2 has identified itself in its discovery signal detectionmessage, the first user equipment UE1 sends the identification to thenetwork and receives corresponding authentication information fortransmission to the second user equipment UE2. Such authenticationinformation contains, for example, a challenge based on a shared secretof the network and of the second user equipment UE2 and/or otherencryption information.

The second user equipment UE2 sends 320 to the first user equipment UE1an association response. In this association response the UE2 can alsosend an authentication response to the network 120 in an exampleembodiment in which the first user equipment UE1 had already startedauthentication process for the second user equipment UE2. Alternatively,the first user equipment UE1 can send 330 to the network 120 anauthentication request with identification of the second user equipmentUE2 and receives 340 an authentication response with possible securityinformation and information on cellular services for passing 350 to thesecond user equipment UE2.

Regardless how the second user equipment UE2 is authenticated to thenetwork 120, the second user equipment UE2 finally has all the usualcredentials for cellular service usage, based on the shared secret knownby the second user equipment UE2 and the network 120. In this context,in sake of simplicity, the user equipment is assumed to contain also apossibly separately formed subscriber identification module such as aSIM or USIM card. Armed with these credentials, the second userequipment UE2 can subsequently send 360 a cellular service request forforwarding 370 by the first user equipment UE1 to the network 120. Acellular service response 380 is sent 380 by the network to the firstuser equipment UE1 that forwards 390 the cellular service response tothe second user equipment 130.

The requesting cellular service and receiving response can be performedfor a large number of times. For instance, if a telephone or video callis established, a great number of data packets can be sent back andforth over the first user equipment UE1. For reducing requiredsignaling, the network 120 may define given slots or channels forrelayed communications between the network 120 and the second userequipment UE2 over the first user equipment UE1. Then, the first userequipment UE1 will automatically forward any information received onthese slots or channels.

FIG. 4 shows a flow chart illustrating an example embodiment of theinvention. In FIG. 4, the second user equipment UE2 sends 410 adiscovery signal transmission. The first user equipment UE1 detects 420the discovery signal and sends 430 to the second user equipment adiscovery detected signal 430. The second user equipment can thennegotiate 270 cellular access via device to device link and access 280cellular service via the first user equipment UE1 as discussed in theforegoing with reference to FIG. 2.

While not drawn, in an example embodiment, the network 120 must firstcontrol the first user equipment to enable device to device discoveryprocessing before the first user equipment starts to listen to discoverysignal transmissions. The network 120 can also indicate particulars suchas timing or other channel information indicative of possible discoverysignal transmission opportunities given to user equipment that maybroadcast discovery signal transmissions.

In an example embodiment, the network 120 also has to enabletransmission of the discovery signal transmissions. In order to be ableto convey such instructions to the user equipment, the network 120 canbe configured to instruct each user equipment to enable discovery signaltransmissions on detecting that such user equipment is about to leavethe coverage area of the network 120. In another example embodiment, theuser equipment can be provided with general enablement to transmitdiscovery signal transmissions if not able to receive signals from thenetwork 120. Such general enablement can be used to prevent completemuting of user equipment that leaves the coverage too sudden for thenetwork 120 to react by sending control instructions or that leaves thecoverage when not operating (e.g. switched off by the user).

Instead of performing device discovery using cellular radio transmittersand receivers, the user equipment are configured in one exampleembodiment to use a second wireless communication circuitries, such aswireless local area network, Private Mobile Radio (PMR), WiMAX or IEEE802.16 (e.g. IEEE 802.16m-2011), Nokia Instant Community (NIC) orOptical-Wireless (FiWi). In the Nokia Instant Community, for example,one can send a message spreading from device to device and then overmore hops and it is possible to find devices needing help or able tohelp other devices for forming access to cellular services, forinstance. In this case, the initial phase for NIC device to discoveryeach other is not controlled by the PLMN operators. Instead, the deviceto device discovery can be performed independently. The network can beinformed of found peer device only if the found peer device needs accessto cellular services. In case of optical communication, the network neednot necessarily control the device to device communications for avoidinginterference to the PLMN network itself. However, even then in anexample embodiment, the network controls the device to devicetransmission permissions to avoid undue congestion.

The user equipment can be informed in various ways of the variousdetails related to performing the device to device discovery andcommunication under control of the network. In one example embodiment,the data are stored beforehand on manufacture of the user equipmentand/or on software updates. In another example embodiment, the userequipment periodically, on external triggering or on-demand retrieve thedata e.g. from the server 190 shown in FIG. 1.

Selection of user equipment that operates as a bridge or mobile relaystation for the out-of-coverage user equipment can be performed in anumber of different ways. In one example embodiment, the discoverysignal transmissions are configured to enable identification of theirsenders. For example, the discovery signal transmissions comprise anidentification of the transmitting user equipment, a random code,session identifier, and/or the network controls the timing or channelsused by each sending user equipment so that the receiving user equipmentout of coverage can indicate in its response a given user equipment foruse as a bridge for accessing the cellular service. The identificationmay comprise a device to device discovery identifier stored in a networkserver such as the server 190 with an associated identification of theuser equipment or its subscription.

In an example embodiment, the user equipment are configured to detecte.g. from signal strength, signal to noise ratio, bit error rate orother quality indication which user equipment is best suited forbridging the out of coverage user equipment to access the cellularservice. Pilot signals sent by the network can be the signals thestrength or quality of which is to be estimated. Then the best suiteduser equipment is made to act as the bridge. By acting as a bridge orbridging in short reference is made to user equipment providing cellularaccess for assisted user equipment to the network via device to devicecommunication. The assisted user equipment refers to the user equipmentthat gains access to cellular service via the bridging user equipment.

The user equipment is typically battery operated mobile, portable orhandheld device. Operating as a bridge can cause substantially power andeven deplete a battery. In an example embodiment, the user equipment isconfigured to signal its battery status (e.g. battery level and orcharging state i.e. whether the battery is being charged) wheninstructed by the network to prepare or start device discoveryprocessing. In another example embodiment, the user equipment canindicate its battery status to the network on meeting predeterminedcriteria or criterion such as approaching boundary of the coverage area;battery level exceeding a threshold level for sufficient battery levelfor bridging; battery level being below a threshold level for sufficientbattery level for bridging; the user equipment being connected to abattery charger; the user of the user equipment having barred thebridging; the user of the user equipment having indicated desire to usethe user equipment for the bridging.

The user equipment selection can also be subjected to available datarates of available user equipment. For instance, some user equipment maybe capable of higher data rates than others and some user equipment mayhave ongoing data connections which leave little or no data transfercapacity.

The bridging user equipment and the out of coverage user equipment, suchas UE1 and UE2 in FIG. 1, can be subscribing to same PLMN.Alternatively, they may be subscribing to different PLMNs. In an exampleembodiment, the network is charging a subscription of the assisted userequipment for the connections and/or data transferred. If the userequipment are subscribing to different PLMNs, the charging can beperformed as if the assisted user equipment were normally roaming to thePLMN of the bridging user equipment. In an example embodiment, datarates available for connections of the assisted user equipment areprovided as defined for the assisted user equipment. If greater than themaximum data rate of the bridging user equipment's subscription wouldenable, the PLMN of the bridging user equipment can allow increasing thedata rate beyond the normal maximum to an extent possible and necessaryfor the assisted user equipment.

Privacy of the assisted user equipment can be protected in a number ofways. In an example embodiment, the communications between the assisteduser equipment and the bridging user equipment are encrypted using theshared secret known by the network and the assisted user equipment.Thus, the assisting user equipment cannot decrypt these communicationsor display or present to its user. For power saving, thesecommunications need not even be further encrypted as other informationtransferred between the bridging user equipment and the network.

The network controlled device discovery need not always lead intoaccessing cellular services by the assisted user equipment. In anexample embodiment, the network controls when and how the user equipmentcan perform device discovery and device to device communication. Also inthis case, the network can control the use of radio resource of the PLMNin question, if the user equipment communicate(s) using their cellulartransmitters and receivers.

Network controlled device discovery may reduce power consumption, reduceradio interference and reduce adverse effects on maximum data throughputof user equipment by controlling only selected user equipment tobroadcast or monitor device to device discovery signals. Other userequipment need(s) not broadcast or monitor the device to devicediscovery signals.

FIG. 5 shows a block diagram of an apparatus 500 suited for operating asthe user equipment 130 or 160 of FIG. 1. In an example embodiment, theapparatus 500 is, comprises, or is comprised by one of the following: amobile telephone; a laptop computer; a personal digital communicationdevice; a game console; a navigation device; a vehicle navigationdevice; fixed cellular telecommunication device; a portable cellulartelecommunication device; an electric book; and a tablet computer.

The apparatus 500 comprises some or all of the following functionalelements: a processor 510; a wireless communication interface 520comprising a first transmitter and receiver or transceiver 525 such as aPLMN compatible transceiver; a memory 540 comprising program code 550and parameter data 560; a positioning circuitry 570; and a userinterface 580. In an example embodiment, the wireless communicationinterface 520 further comprises a second transmitter and receiver ortransceiver 530 such as a wireless local area network (WLAN); PrivateMobile Radio (PMR); and/or WiMAX or IEEE 802.16 (e.g. IEEE 802.16m-2011)compatible transceiver. The second transmitter and receiver ortransceiver 530 can be used e.g. for device to device discovery and/orcommunication using a radio system other than the PLMN and/or for othercommunications. The processor 510 can be configured to control generaloperations of the apparatus 500 according to the program code 550 andthe parameter data 560. In addition to any of the aforementionedelements, the apparatus 500 can comprise other functional elements suchas a power supply and chassis.

In one example embodiment, the parameter data 560 contains a device todevice identifier. The device to device identifier may at simplest be asubscriber number, International Mobile Subscriber Identity (IMSI),Temporary International Mobile Subscriber Identity (TIMSI), GloballyUnique Temporary UE Identity (GUTI). Alternatively, a particular deviceto device identifier or D2D identifier in short can be assigned for thepurpose of device to device discovery and addressing of device to devicemessages. The D2D identifier can be defined by the user each userequipment, by the user equipment or by a network element. The D2Didentifier need not necessarily be globally unique. However, foravoiding ambiguity and potential errors in addressing and forsimplifying authentication to the PLMN, an example embodiment makes useof a D2D identity database accessible to the PLMN operator of the userequipment subscriptions in question. For instance, the server 190 can beconfigured to store the D2D identity database.

In an example embodiment, the D2D identity database comprises for eachof a plurality of user equipment a D2D identifier with an associatedglobally unique identifier of subscriber e.g. in form of subscribernumber or IMSI. Alternatively, the associated identifier can be a deviceidentifier of the user equipment, such as an International MobileEquipment Identity (IMEI). By making available to the PLMN theassociated subscription identification, the PLMN can identify anassisted user equipment from its D2D identifier on receiving the D2Didentifier e.g. as part of the process illustrated with reference to anyof FIGS. 2 to 4.

FIG. 6 shows a block diagram of an apparatus 600 suited for operating asa network element such as base station or base station controller. Itshall be appreciated that the apparatus can be formed of discreteelements some of which reside at other sites and in remote device ordevices.

The apparatus 600 comprises some or all of the following functionalelements: a processor 610; a user interface 620; a transmitter andreceiver or transceiver 630; a memory 640 comprising program code 650and parameter data 660; and a mass memory 670 with a database 680comprising e.g. measurement data, information on currently operatingbridging user equipment, available devices for acting as bridging userequipment and coverage information of the network. The processor can beconfigured to control general operations of the apparatus 600 accordingto the program code 650 and the parameter data 660. The apparatus 600further comprises an input/output circuitry 690 for communicating withother network elements. In addition to any of the aforementionedelements, the apparatus 600 can comprise other functional elements suchas a power supply and chassis.

Embodiments of the present invention may be implemented in software,hardware, application logic or a combination of software, hardware andapplication logic. In an example embodiment, the application logic,software or an instruction set is maintained on any one of variousconventional computer-readable media. In the context of this document, a“computer-readable medium” may be any media or means that can contain,store, communicate, propagate or transport the instructions for use byor in connection with an instruction execution system, apparatus, ordevice, such as a computer, with examples of a computer described anddepicted in FIGS. 5 and 6. A computer-readable medium may comprise acomputer-readable storage medium that may be any media or means that cancontain or store the instructions for use by or in connection with aninstruction execution system, apparatus, or device, such as a computer.

If desired, the different functions discussed herein may be performed ina different order and/or concurrently with each other. Furthermore, ifdesired, one or more of the before-described functions may be optionalor may be combined.

Although various aspects of the invention are set out in the independentclaims, other aspects of the invention comprise other combinations offeatures from the described embodiments and/or the dependent claims withthe features of the independent claims, and not solely the combinationsexplicitly set out in the claims.

It is also noted herein that while the foregoing describes exampleembodiments of the invention, these descriptions should not be viewed ina limiting sense. Rather, there are several variations and modificationswhich may be made without departing from the scope of the presentinvention as defined in the appended claims.

1-55. (canceled)
 56. An apparatus comprising: a wireless communicationinterface configured to exchange information with a public land mobilenetwork; and at least one processor configured to control operation ofthe apparatus; wherein the at least one processor is configured todetect a device to device discovery initiation instruction from thepublic land mobile network and to responsively: cause the wirelesscommunication interface to send one or more discovery signaltransmissions for a peer device or to monitor discovery signaltransmissions sent by a peer device; and to cause communicatingdirectly, using the wireless communication interface, with a peer devicethat indicates having received the discovery signal transmission or fromwhich the apparatus has detected a discovery signal transmission inresult of the monitoring of discovery signal transmissions.
 57. Theapparatus of claim 56, wherein the at least one processor is furtherconfigured to cause the wireless communication interface to sendmeasurement information to the public land mobile network.
 58. Theapparatus of claim 57, wherein the apparatus further comprises a batteryfor operating the apparatus and the measurement information comprises abattery status.
 59. The apparatus of claim 56, wherein the at least oneprocessor is further configured to detect a discovery mode request fromthe public land mobile network to start operating in a discovery mode.60. The apparatus of claim 59, wherein the at least one processor isfurther configured to subject the detecting of the discovery moderequest to identifying an identifier of the apparatus or associatedsubscription in the discovery mode request.
 61. The apparatus of claim59, wherein the at least one processor is further configured to subjectthe detecting of the discovery mode request to determining whether givenone or more criteria are met.
 62. The apparatus of claim 61, wherein theat least one processor is further configured to obtain from thediscovery mode request the given one or more criteria.
 63. The apparatusof claim 61, wherein the given one or more criteria define a geographicregion or a signal strength threshold for given downlink signals. 64.The apparatus of claim 59, wherein the at least one processor is furtherconfigured to cause the wireless communication interface to send one ormore discovery advertisement signals in response to the detecting of thediscovery mode request.
 65. The apparatus of claim 64 wherein the atleast one processor is further configured to cause containing of adevice to device discovery identifier of the apparatus in the one ormore discovery advertisement signals.
 66. The apparatus of claim 59,wherein the at least one processor is further configured to cause thewireless communication interface to start to monitor discoveryadvertisement signals in response to the detecting of the discovery moderequest.
 67. The apparatus of claim 56, wherein the at least oneprocessor is further configured to connect with an assisted device thatis found in the discovery mode.
 68. The apparatus of claim 67, whereinthe at least one processor is further configured to cause exchanging anauthentication request and response between the apparatus and theassisted device.
 69. The apparatus of claim 67, wherein the at least oneprocessor is further configured to cause exchanging authenticationsignaling between the assisted device and the public land mobile networkfor allowing the assisted device to authenticate to the public landmobile network.
 70. A method comprising: exchanging wirelessly by anapparatus information with a public land mobile network; detecting bythe apparatus a wireless device to device discovery initiationinstruction from the public land mobile network and responsively: sendby the apparatus one or more wireless discovery signal transmissions fora peer device or monitor wireless discovery signal transmissions sent bya peer device; and directly communicate wirelessly by the apparatus witha peer device that indicates having received the wireless discoverysignal transmission or from which the apparatus has detected a wirelessdiscovery signal transmission in result of the monitoring of wirelessdiscovery signal transmissions.
 71. The method of claim 70, furthercomprising wirelessly sending by the apparatus measurement informationto the public land mobile network.
 72. The method of claim 71, whereinthe apparatus further comprises a battery for operating the apparatusand the measurement information comprises a battery status.
 73. Themethod of claim 70, further comprising detecting by the apparatus adiscovery mode request from the public land mobile network to startoperating in a discovery mode.
 74. The method of claim 73, furthercomprising subjecting by the apparatus the detecting of the discoverymode request to identifying of an identifier of the apparatus orassociated subscription in the discovery mode request.
 75. An apparatuscomprising: a processor configured to cause the apparatus to: exchangewirelessly information with a public land mobile network; detect awireless device to device discovery initiation instruction from thepublic land mobile network and responsively: send one or more wirelessdiscovery signal transmissions for a peer device or monitor wirelessdiscovery signal transmissions sent by a peer device; and communicatewirelessly directly with a peer device that indicates having receivedthe wireless discovery signal transmission or from which the apparatushas detected a wireless discovery signal transmission in result of themonitoring of wireless discovery signal transmissions.